Arrhythmia takes place mainly due to formation of erethism at the heart and abnormal transfer of the formed erethism. From the standpoint of prognosis, the symptom of arrhythmia includes various cases ranging from cases which can be left without treatments to fatal cases. Arrhythmia causing degradation in the quality of life is treated for curing. Antiarrhythmic drugs such as Na channel blocking agent and K channel blocking agent were mainly used before. In 1982, the myocardial cautery using an ablation catheter was applied to the clinical treatment as a non-medicinal therapy. At present, development of a novel antiarrythmia drug is continued and, at the same time, improvement in the myocardial cautery is also continued.
In the percutaneous myocardial cautery, ablation catheters are inserted into the cardial cavity, and the tissue of the cardial muscle where the arrhythmia originates is destroyed or modified by applying heat between a tip electrode and an opposite electrode plate. This treatment is mainly applied to tachyarrhythmias such as paroxysmal supraventricular tachycardia, atrial tachycardia, atrial flutter and paroxysmal venticular tachycardia. As the first step, the cause of arrhythmia and the region of arrhythmia are investigated by the cardiac electrophysiological examination. The type and the circuit of arrhythmia are confirmed, and the optimal region for passing electric current is decided based on the result of the investigation. In the myocardial cautery, the tip electrode is pushed to the region causing the arrhythmia, and heating at 53 to 60° C. for about 60 seconds, for example, is repeated.
The spherical electrode having a single spherical shape shown in FIG. 11 and the cylindrical electrode having a spherical tip shown in FIG. 12, which are used widely at present, have small diameters and exhibit excellent operability. However, these electrodes have drawbacks in that the output power is small, the electrode cannot be brought into contact with or fixed to the organism sufficiently, the degree of cooling with the circulating blood stream is small, and cauterization is limited to the range of about 5 mm around the region pushed by the tip electrode. Therefore, these electrodes can be applied only to the treatment of monophyletic arrhythmias having a single cause the origin of which can be found in a narrow range and to the treatment of a conduction path passing through a very narrow portion. Application to deep regions in the ventricular wall is difficult although regions relatively close to the endocardium in the ventricular wall can be cauterized. Tip electrodes having two electrodes shown in FIGS. 13 and 14 are proposed. However, the effect of improvement in the contact with organisms and the cooling with the circulating blood stream is insufficient. Electrodes having a great dimension which are called large tip electrodes cause a decrease in the operability due to the great diameter of the electrode although the output power is great and the cooling with the circulating blood stream is improved. Therefore, an ablation catheter which has an electrode having a small diameter, exhibits excellent operability and can provide a great output power has been desired.
The present invention has an object of providing an ablation catheter having a tip electrode which has a small diameter, is brought into excellent contact with organisms, can provide a great output power and is easily cooled with the circulating blood stream.